Performance Evaluation of A Low Heat Rejection Diesel Engine for

Transcription

Pamukkale Üniversitesi
Mühendislik Bilimleri Dergisi
Cilt 16, Sayı 1, 2010, Sayfa 87-94
Performance Evaluation of A Low Heat Rejection Diesel Engine
for Different Insulation Levels
Farklı İzolasyon Seviyeleri İçin Düşük Isı Kayıplı Bir Dizel Motorunun
Performans Değerlendirmesi
Can HAŞİMOĞLUa*, Murat CİNİVİZb ve M. Sahir SALMANc
a
Sakarya University, Technical Education Faculty, Mechanical Education Department, 54187, Sakarya
b
Selcuk University, Technical Education Faculty, Mechanical Education Department, 42031, Konya
c
Gazi University, Technical Education Faculty, Mechanical Education Department, 06503, Ankara
Geliş Tarihi/Received : 29.05.2009, Kabul Tarihi/Accepted : 09.09.2009
ABSTRACT
This experimental study focuses on investigating of effects of low heat rejection engine application to a
diesel engine at different insulation levels. For this purpose cylinder head and valves of the test engine were
thermally insulated with yttria-stabilized zirconia (Y2O3–ZrO2) layer at first stage. Then in addition to cylinder
head and valves, pistons of the test engine were coated with the same material. Brake specific fuel consumption
(BSFC), exhaust gas temperature (EGT), brake thermal efficiency and volumetric efficiency of the test engine
were investigated for two different insulation levels. After the engine tests it was determined that BSFC was
improved by 4 - 7.1 %, EGT was increased by 3.5 - 6.8 %, brake thermal efficiency was improved by 4.1-7.9 %
and volumetric efficiency was increased by 0.9 - 2.6 % with LHR application. It was also determined that these
improvements in engine performance are proportional with the insulation levels of the test engine.
Keywords : Low heat rejection engine, Thermal barrier coating, Diesel engine, Engine performance.
ÖZET
Bu deneysel çalışma bir dizel motoruna farklı izolasyon seviyelerindeki düşük ısı kayıplı motor uygulamasının
etkilerinin incelenmesine yöneliktir. Bu amaçla ilk aşamada deney motorunun silindir kapağı ve supapları
termal bariyer oluşturmak için yitriya ile stabilize zirkonya (Y2O3–ZrO2) ile kaplanmıştır. Daha sonra silindir
kapağı ve supaplara ilaveten deney motorunun pistonları da aynı malzeme ile kaplanmıştır. Deney motorunun
özgül yakıt tüketimi, egzoz gaz sıcaklığı, fren ısıl verimi ve hacimsel verimi iki farklı izolasyon durumu için
incelenmiştir. Düşük ısı kayıplı motor uygulaması ile motor testlerinin sonucunda özgül yakıt tüketiminde
% 4-7,1 iyileşme, egzoz gazı sıcaklıklarında % 3,5–6,8 artış, fren ısıl verimde % 4,1–7,9 iyileşme ve hacimsel
verimde % 0,9–2,6 artış tespit edilmiştir. Ayrıca motor performansındaki bu iyileşmelerin deney motorunun
izolasyon seviyesi ile orantılı olduğu belirlenmiştir.
Anahtar Kelimeler: Düşük ısı kayıplı motor, Termal bariyer kaplama, Dizel motoru, Motor performansı.
1. INTRODUCTION
by the maximum temperature that combustion
chamber components such as piston, cylinder head
and valves, can withstand. Hence, low heat rejection
engines become popular as they allow the use of
higher combustion temperatures. Engine which
is insulated to reduce the rejected heat through
its cooling system is known as Low Heat Rejection
(LHR) Engine (Zhou, 1995; Çengel and Boles, 1996;
Beard, 2006; Giakoumis, 2007).
Turbocharged diesel engines are generally preferred
as prime mover from light to heavy duty applications
due to their high reliability and fuel economy.
However, rapid depletion of fossil based fuel reserves
has focused the researches on improving fuel
economy further. Thermodynamic considerations
declared that raising the highest temperature in a
cycle also raises the thermal efficiency of the engine.
The highest temperature in the cycle is limited
* Yazışılan yazar/Corresponding author. E-posta adresi/E-mail address : [email protected] (C. Haşimoğlu)
87
C. Haşimoğlu, M. Ciniviz ve M. S. Salman
Table 1. Specifications of the test engine.
The heat rejected through the cooling system
is a precursor of inefficiency. If the combustion
chamber components are insulated thermally,
thermal efficiency of the engine may be improved.
However, this may cause problem due to thermal
resistance of hot section components in the engine.
In order to improve the reliability and durability of
hot section metal components in advanced engines
and enhance engine performance, thermal barrier
coatings (TBCs) were applied on the surface of
these components. The use of TBCs can result in a
significant temperature decrease between the hot
gas and the surface of these components. TBCs are
multilayer systems consisting of a metallic bond coat
a stabilized zirconia top coat (to provide the thermal
barrier) and an intermediate alumina protective
layer that forms during high temperature exposure
(Zhou, 1995; Zhou et al., 2007; Sidhu et al., 2007).
Engine Type
Mercedes-Benz OM364A
Number of cylinders
Displacement (l)
4
3.972
Compression ratio
Max. engine power (kW)
17.25/1
66@2800 rpm
Max. engine torque (Nm)
266@1400 rpm
The constant-speed various-load tests were
performed for engine speeds of 1400 and 2800 rpm.
The fuelling rate and, hence, the load (between
40 and 200 N m with increments of 40 Nm) was
varied at each engine speed. The dynamometer
load was measured using a load cell. The load cell
was calibrated with standard weights. The engine
speed was measured by an optical sensor. Both the
engine speed and the load values were collected by
a data acquisition system and then recorded by a
computer. The hydraulic dynamometer was rated for
999 N m maximum torque and 7500 rpm maximum
operating speed having accuracies of 0.1 N m and 1
rpm respectively. Exhaust gas temperature before
the turbine inlet was measured by NiCr-Ni type
thermocouples. Fuel consumption was measured
with a digital scale. It had a maximum capacity
of 8 kg and a precision of 0.1 g. Air consumption
was measured with an air flow meter. Exhaust
gas temperature (EGT), fuel and air consumption
values were recorded manually during the tests.
Measurements were taken after reaching the working
temperature of the engine. The uncertainty of the
measured parameters is important for verifying the
accuracies of the test results. The uncertainties of the
measured and calculated parameters are shown in
Table 2.
The LHR engine technology has the potential for
gains in fuel efficiency, increased power density,
reduction in cooling system size, reduced noise,
higher exhaust gas energy, ability to operate on
lower cetane fuels. With in the LHR engine concept
some of combustion chamber elements are coated
with high temperature resistant ceramic material.
The ceramic coated engine parts are pistons, cylinder
head, valves, cylinder liners and exhaust port
(Zhou, 1995; Parlak et al., 2004; Parlak et al., 2005).
Since 1970s many studies have been done about
LHR engines. Due to the increased exhaust gas
temperatures
turbocharged
diesel
engines
have been preferred. However, as there is no
standard about LHR engine design, the results
from these studies may contradict each other
(Gatowski, 1990; Sun, 1994; Yaşar, 1997; Haşimoğlu,
2005). This study has two aspect one is to determine
the loss or benefits of LHR application and the other
is to determine the effect of insulation level to them.
For these purpose performance characteristics of a
turbocharged LHR diesel engine was evaluated for
two different insulation levels.
Table 2. The uncertainties of the measured and
calculated parameters.
Parameter
BSFC
EGT
Brake thermal efficiency
Volumetric efficiency
2. EXPERIMENTAL APPARATUS AND
PROCEDURE
Errors (%)
1.00
0.28
1.00
0.23
First test of standard (STD) engine were done. Then,
cylinder head and valves of the test engine were
coated with atmospheric plasma spray coating
method to obtain LHR1 engine. Before the coating
process, material 0.5 mm thick was removed from
surfaces by machining to keep the compression
ratio of the LHR1 engine the same as that of the STD
engine. As for plasma gas, a mixture of Ar + 5 % H2
was used. The cylinder head and valves were coated
with yttria-stabilized zirconia (Y2O3–ZrO2) layer 0.35
mm thick over a nickel – chromium –aluminum
bond coat 0.15 mm thick. The Y2O3–ZrO2 was chosen
as the ceramic material because of its durability
in a high-temperature environment. The coating
was applied with the plasma spray method, as this
The experiments were performed in a turbo charged
direct injection diesel engine. Some important
specifications of the test engine are given in
Table 1 and schematics of the test set up can be seen
in Figure 1. Other major part of the experimental setup is a hydraulic dynamometer (Go-Power Dt 100)
which is used to load the engine.
Pamukkale University, Journal of Engineering Sciences, Vol. 16, No. 1, 2010
88
Performance Evaluation of A Low Heat Rejection Diesel Engene for Different Insulation Levels
method was both economic and easy to accomplish.
After completing the test of LHR1 engine (cylinder
head and valves coated engine), pistons of the test
engine were coated with the same procedure as
mentioned above. So LHR2 engine (cylinder head,
valves and piston coated engine) was obtained.
Same test procedure was applied to LHR2 engine.
And the results for STD, LHR1 and LHR2 engine were
compared.
Figure 1. Schematics of test set-up.
3. EXPERIMENTAL RESULTS AND
DISCUSSION
engine) and engine cylinder head, valves and piston
coated engine (LHR2). Comparisons were done
according to non insulated engine.
The experimental results of brake specific fuel
consumption (BSFC), exhaust gas temperature (EGT),
brake thermal efficiency and volumetric efficiency
values by engine load are given as graphics in
Figure 2 to 9. There are there insulation levels in the
experiments: non insulated engine (STD engine),
cylinder head and valves coated engine (LHR1
As can be seen from Figure 2-3, BSFC was decreased
with increased engine load generally. Reduction in
BSFC was increased as the insulation level increased.
For LHR1 and LHR2 engine BSFC was decreased by 4
and 6.7 % at 1400 rpm and decreased by 4 and 7.1 %
for 2800 rpm, respectively.
Pamukkale Üniversitesi, Mühendislik Bilimleri Dergisi, Cilt 16, Sayı 1, 2010
89
Figure 2. Comparison of BSFC by engine load at 1400 rpm.
Figure 3. Comparison of BSFC by engine load at 2800 rpm.
Kvernes et al., (1990) were determined 5 % reduction
in fuel consumption of a medium duty LHR diesel
engine which’s pistons and valves were coated with
0.5 mm thick partially stabilized zirconia. (Büyükkaya
et al., 2006) obtained 1-6 % reduction in BSFC of a
six cylinder, direct injection (DI), turbocharged LHR
diesel whose pistons, valves and cylinder head were
coated with magnesia stabilized zirconia (MgZrO3).
Also, (Parlak et al., 2003) was reduced BSFC of a
single cylinder, pre-combustion chamber LHR diesel
engine by 3 % with coating of cylinder head, valves
and piston 0.35 mm thickness of MgO–ZrO2 over a
0.15 mm thickness of NiCrAl bond coat. (Sun et al.,
1994) reported that diffusion burning period of
LHR diesel engine increases while diffusion burning
and ignition delay periods shorten in comparison
to standard diesel engines. So oxidation of fuel will
be improved due to thermal insulation during LHR
combustion and BSFC decreases.
The EGT before turbine inlet was increased with the
increase of engine load generally (Figure 4-5). The
EGT values were increased with the increasing of
insulation level. For LHR1 engine EGT was increased
by 3.5 to 6.3 %, for LHR2 engine EGT was increased
by 5.2 to 6.8 % at 1400 rpm. At 2800 rpm, EGT was
increased by 5.3 to 6.8 % for LHR1 engine, for LHR2
engine EGT was increased by 17.9 to 19.6 %. (Parlak,
2005) was measured that EGT of an indirect injection
(IDI) diesel engine was increased by 11-22.8 % with
LHR application. (Yaşar et al., 1996) were declared
that EGT of a DI turbocharged LHR diesel engine was
increased by 5-13 %.
90
Figure 4. Comparison of EGT by engine load at 1400 rpm.
Figure 5. Comparison of EGT by engine load at 2800 rpm.
The increase of EGT temperature in LHR conditions
may be explained in two ways: One is the decreasing
of the heat loss to the cooling system, and the other
is the increasing of the total combustion duration
in LHR engine. The increase of total combustion
duration causes extending of the combustion
into the exhaust process, thus leading to the
exhaust temperature increases (Reddy et al., 1990;
Sun et al., 1994; Parlak, 2005).
engine was improved (Figure 6-7). At 1400 rpm,
brake thermal efficiency of LHR1 and LHR2 engine
was increased by 4.2 and 7.3 %, respectively. At 2800
rpm, brake thermal efficiency of LHR1 and LHR2
engine was increased by 4.1 and 7.9 %, respectively.
(Parlak et al., 2005) obtained 2 % increment in
brake thermal efficiency with LHR application to
a six cylinder DI turbocharged diesel engine. Due
to the reduction of BSFC with LHR application, the
brake thermal efficiency {ηt = (3.6 x 106) / (be x Hu),
be - specific fuel consumption (g/kWh), Hu- lower
heating value of test fuel (kJ/kg)} was increased.
Generally, brake thermal efficiency was increased
with the increasing engine load. As the insulation
level increased, brake thermal efficiency of the test
91
Figure 6. Comparison of brake thermal efficiency by engine load at 1400 rpm.
Figure 7. Comparison of brake thermal efficiency by engine load at 2800 rpm.
The volumetric efficiency of test engine was
increased with increased engine load. The
volumetric efficiency was improved as the insulation
level increased (Figure 8-9). While the volumetric
efficiency of LHR1 engine was improved by 1 %,
LHR2 engine’s volumetric efficiency was improved
by 2.5 %, at 1400 rpm. At 2800 rpm, the efficiency
of LHR1 and LHR2 engine was improved by 0.9 and
2.6 %, respectively. (Yaşar et al., 1996) declared that
volumetric efficiency of a DI turbocharged diesel
engine was improved by 3 % with LHR application.
The improvement of the volumetric efficiency in
LHR engines can be attributed to the higher EGT.
Therefore, the turbocharger will induce more air to
the cylinders, so the volumetric efficiency will be
increased in LHR operations.
92
Figure 8. Comparison of volumetric efficiency by engine load at 1400 rpm.
Figure 9. Comparison of volumetric efficiency by engine load at 2800 rpm.
4. CONCLUSIONS
After the experiments it was determined that all
performance parameters investigated in this study
were improved with LHR application. Also, the
improvement level was increased as the insulation
level of the test engine was increased.
total combustion duration in LHR engines, average
in-cylinder gas temperature increases when
exhaust valve opens. Consequently, the increase of
in-cylinder temperature levels and the extending
of combustion duration in LHR conditions cause to
increase in EGT before turbine inlet.
Due to the increasing of diffusion burning period in
LHR combustion, more fuel will be oxidized in this
period. This improves combustion process in LHR
engine so BSFC of LHR engines get better.
Brake thermal efficiency is a measure of engine’s
capability to convert fuel’s chemical energy to useful
work. As the BSFC of LHR engines were decreased
the brake thermal efficiency was improved.
With thermal insulation less heat would be transferred
to cooling system thus in-cylinder temperature
levels would increase. Besides the extending of
The increase of EGT in LHR engines augmented the
energy which turbocharger can be extracted from
the exhaust gases. Thus the turbocharger could
93
6. ACKNOWLEDGEMENTS
induce more air to engine’s cylinders and volumetric
efficiency improved in LHR engines.
The authors would like to thank Gazi University
Scientific Research Council for supporting of this
study under Project No. 07/2003–18.
5. NOMENCLATURE
BSFC
: Brake specific fuel consumption
EGT
: Exhaust gas temperature
LHR
: Low heat rejection
STD
: Standard
TBC
: Thermal barrier coating
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of the Diesel cycle and exergy of the exhaust gas stream
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Performance Evaluation of A Low Heat Rejection Diesel Engine for

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